1) Field of the Invention
This invention relates to animated displays used in advertising, merchandising, instructional and educational fields. It is related to displays using light polarisation effects in order to illustrate movement of various objects, flow of liquids or flow of energy in systems that are graphically or artistically depicted on a backlighted or frontlighted screen or are projected on a separate screen. The animation effects can include linear, curved, wavelike, rotational, pulsating, accelerating, decelarating, blinking and the like effects and the effects can be limited to the parts on the display screen to be animated. This invention also relates to means of selectively illuminating limited areas on a dark screen such as used, for example, in indicators, signals and advertising panels. Information in forms of pictures, artwork symbols, letters, alphanumerics that is fixed or changed as a function of a measured quantity can form a part of an animated display or form a separate display device such as an indicator, meter or monitor of any physical quantity that may or may not include an animated arrow or other picture to draw attention. This invention also relates to colored displays animated and/or stationary in which the color or color change is obtained through the interaction of polarised light with a chromatic polariser.
2) Description of Prior Art
The now commercially available polarising mosaic is defined next for the purpose of describing and claiming the invention. The preferred definition is an assembly of achromatic or chromatic linear polariser segments having different angles of polarisation placed side by side that forms one sheet by suitable bonding techniques. In an alternative form known in the art and commercially available, as disclosed in the book by W. A. Shurcliffe entitled: "Polarised Light", Harvard University, 1962 and in the patent by Siksal such segments can be embossed on a plastic sheet, thus modifying the birefringence, dichroism or chromaticity of these sheets, which, when bonded to another polariser sheet fulfills the same function with the same results as the assembly of polariser segments.
In the prior art animated displays of the type outlined in the foregoing have been generally characterised by the presence of a a lights source, a rotable polariser, manually or motor driven and a polarising mosaic as defined above. One such display device is disclosed in the patent by Yates and another, which might be considered an improvement on the former, is disclosed in the patent to A. Siksal, cited. Both show a motor driven polariser disc being an integral and necessary part of the system. In the prior art devices capable of selectively illuminating parts of a dark screen, using the light polarisation phenomena applied to indicators or advertising panels, also relied on rotating parts as disclosed for example in the patent to Dreyer. In the prior art production of animated color effects or selectively illuminated colored parts on the viewing screen has been obtained by placing suitably oriented and shaped birefringent or dichroic plastic material between two polarisers (the second being often referred as the analyser), one of them being usually a motor driven polariser disc. An example of such a display is disclosed in the patent to Burchell.
The presence of mechanical often motor driven parts in the prior art displays and indicators discussed in the foregoing gives rise to a number of undesirable side effects. In addition to wear and tear, that calls for regular maintenance, it is necessary to control some noise, vibration and heat generation due to the operation of an electric motor. Also, since a rotating disc is usually circular in shape and the display panel usually square or rectangular, a common problem arising is that of illuminating the corners and edges of the panel with rotating polarised light. Additional pulleys and discs have to be provided for the corners; they do not solve the problem completely and add to the complexity of the design. Although the speed of the motor is controllable, it cannot be changed quickly enough to produce certain desired animation effects. The range of possible animation effects could be greatly enlarged and the process could be simplified were it possible to animate individually the desired portions of the display. However the speed of the motor in such displays often determines the rate of change of the animation effects throughout the whole display panel. The above mentioned limitations of prior art devices can be overcome and a number of advantages and new animation effects can be realised by the present invention. They will be explained in the parts of the specifications to follow.